Hierarchical routing and network summarization are approaches realized in order to solve scalability issues for routing in a multi-domain scenario. The global topology of a multi-domain network comprising a huge number of nodes can cause scalability issues.
A hierarchical path calculation element (H-PCE) for multi-domain scenario is described in IETF RFC-4655 and IETF RFC 6805. In this model there are two levels of path computation. The high level is named Parent PCE (P-PCE) and it is responsible for end-to-end (E2E) path computation determining the sequence of the domain to cross, while the low level is called a child PCE (C-PCE). C-PCE is responsible for computing the internal path of the controlled domain that is associated with the E2E path computation of the parent domain.
A H-PCE can perform multi-domain path computation in different ways. One of such ways is creating a virtual topology where a Parent PCE computes E2E paths. The virtual topology is fed by a C-PCE a set of summarized information of the physical domain.
Hierarchical routing allows providing one or more abstraction layers to the network, so that the routing tasks can be performed by more entities (e.g. PCEs), and in parallel. In some examples of networks, the visibility of the network is layered, so that each layer deals with a smaller (e.g. technology-specific) network.
Summarization, in a multi-domain context, is a way to depict a network physical resources set with a logical network, in order to reduce the amount of topology information to be distributed through the physical network. This decreases routing computation time and preserves confidentiality of each domain.
Summarization mechanisms allow a reduction in the amount of routing information, as well as signaling information, topology information and network complexity. Moreover, such summarized information can be exported between layers according to the layer-specific needs. In some examples of networks, hierarchical routing is used in a multilayer network, for example, to simplify the amount of information that a server layer exports to client layer.
The combined use of both hierarchical routing and network summarization allows a reduction in the number of resources to be managed and allows the preserving of confidentiality in the multi-domain context. However, a result is a less detailed knowledge of the network resources.
An improved summarization of resources in this context would allow improved end-to-end routing.